Pushbutton for Actuating an Electropneumatic Parking Brake (Eph)

ABSTRACT

Disclosed is a pushbutton ( 5 ), especially for actuating an electropneumatic parking brake (EPH) in road vehicles, which is connected to evaluation electronics (ECU) ( 6 ) via connecting cables ( 1  to  4 ). In order to detect switching processes and/or faults, the input resistance of the pushbutton ( 5 ) between the connecting points ( 7, 8 ) or ( 9, 10 ) is evaluated, thus allowing the evaluation electronics (ECU) ( 6 ) to reliably detect both the switched position of the pushbutton ( 5 ) and potential fault conditions.

The invention relates to a pushbutton, especially for actuating anelectropneumatic parking brake (EPH) in road vehicles, according to thepreamble of claim 1.

An electropneumatic parking brake or parking brake of the general typeunder consideration is described in DE 10336611 A1, for example, and itis used to hold a vehicle, especially a commercial vehicle having apneumatic brake system, safely during a prolonged stoppage by ventingits spring-actuated brake cylinder. By venting of the spring actuator,the brakes, usually of the rear axle, are applied and held withoutfurther input of energy. For this purpose the vehicle can be equippedwith an electronically activated brake system (EBS) or even with a brakesystem that is activated conventionally via a pneumatic controlpressure.

For actuation of the parking brake function, the known pressurized fluidoperated brake system for a vehicle is provided with an electric parkingbrake signal transducer, which is designed as a pushbutton with threepositions (neutral, parking brake and trailer checking position).Detection of faults, such as contact faults or wire breaks of the signaltransducer, as may be required by applicable legal regulations, ispossible to only a limited extent.

Further, DE 19838886 A1 describes an electric parking brake (EPB), inwhich a brake device can be actuated with an operating element forparking a vehicle. Upon actuation of the operating element while thevehicle is stationary, the electric parking brake system is alternatelyapplied and released. The operating element is designed as a pushbuttonwith two positions and one status indicator. This reference does notmention fault checking of the operating element.

Finally, WO 00/29268, which falls into the general class underconsideration, describes a device and a method for controlling anelectrically actuated parking brake. For particularly reliable detectionof the operator's wish concerning actuation of the parking brake, it isproposed here that the input device for receiving the operator's wish beredundantly designed in its individual components and that at the sametime it be monitored by means of an electronic control device. For thispurpose, a plurality of procedures takes place cyclically within anevaluating unit of the control device, in order to permit detection of afault in the input device and also to ensure that the operator's wishcan be recognized. In this way it is possible to react appropriately tofaults that occur and, alternatively, to place the vehicle in a safedriving condition by means of the parking brake even if the operator'swish is not clearly recognized. For this purpose, fault detection ismade possible by measuring potentials across resistors installed in theinput device. A fault is indicated by a signaling device in thedashboard.

The known input device has considerable cabling complexity, namely eightconnecting lines. Furthermore, it has a complex construction of switchesand resistors used and a complex evaluation method for detecting afault. Considerable memory space is needed by the program routinesrequired for this purpose in the evaluating microcontroller.

The object of the present invention is to provide a pushbutton withconnected evaluating electronic unit for actuating an electropneumaticparking brake (EPH), wherein the pushbutton is simplified in terms ofhardware and wherein particularly simple detection of all switchpositions and possible fault conditions is achieved.

This object is achieved by the invention as recited in claim 1. Thedependent claims contain expedient improvements.

Because of the simple evaluation of the potentials of the two connectinglines or of the input resistance of the pushbutton according to theinvention between the terminal points thereof, fault detection isconsiderably simplified compared with the prior art. Cyclic querying ofpotentials of a plurality of resistors by means of program routines isno longer required. Rather, a simple measurement of the potential in theconnecting lines of the pushbutton is sufficient.

The present invention will be described in more detail and furtheradvantages will be pointed out hereinafter on the basis of exemplaryembodiments with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of the outside view of the inventivepushbutton with connecting lines to the evaluating electronic unit(ECU).

FIG. 2 is a schematic diagram of the internal circuit layout of thepushbutton with connected cable to the ECU.

FIG. 3 is a diagram with a representation of the possible correct aswell as faulty output potentials of the pushbutton in its various switchpositions.

FIG. 4 is a diagram of the circuit according to FIG. 2 with additionalwake-up circuit.

FIG. 5 is a simplified configuration of the circuit of the pushbutton.

FIG. 1 schematically illustrates the outer appearance of a pushbutton(5), in this case an EPH pushbutton (5), as well as its connection toevaluating electronic unit (ECU) (6). Pushbutton (5) is mounted in arecess of the dashboard of a commercial vehicle (not illustrated). Foractuation, a rocker (25) is used which can be actuated upward (key T1)as well as downward (key T2) from the indicated neutral position.

As described hereinafter, pushbutton (5) can be used to actuate acompressed-air-operated parking brake. However, it can also be used toactuate differently operated parking brakes, such as hydraulic parkingbrakes.

Key T1 is used for alternately applying and releasing theelectropneumatic parking brake (EPH). Key T2 is used for applying whatis known as the trailer checking position (described hereinafter).

Actuation of keys T1, T2 by the operator is transmitted via four lines(1) to (4) to ECU (6). Two further lines (17, 18) routed back from ECU(6) to EPH pushbutton (5) are used for the return signal (statusindication) of the respective position of the electropneumatic parkingbrake or parking brake (applied or released).

Lines run from ECU (6) to various solenoid valves which are used forcontrol of the parking brake (not illustrated). Such valves as well asthe control of the parking brake achieved thereby are described in moredetail in DE 10336611 A1, for example.

Signals from sensors, especially pressure sensors (not illustrated) mayalso be sent to ECU (6).

A signal light (24) mounted in the EPH pushbutton can be used toindicate the status of the EPH to the operator. However, a separatesignal light (not illustrated) disposed in the dashboard can also beused. This has the advantage that status indication lines (17, 18)between pushbutton (5) and ECU (6) can be dispensed with. The signallight disposed in the dashboard is advantageously connected to theassociated electronic unit, in this case ECU (6), via a data bus, suchas a CAN bus.

FIG. 2 shows the internal construction or the circuitry of EPHpushbutton (5). This comprises two parallel switching groups 1 and 2 ofidentical layout. Because of this redundancy, it is still possible, evenin the case of malfunctions in one switching group, for the ECU torecognize the operator's wish from the signals of the intact switchinggroup.

For simplicity, only switching group 1 will be explained hereinafter.

Switching group 1 is equipped with two resistors R1 and R2, which aredisposed in parallel and can be connected by means of two changeoverswitches (11) and (12) to terminal points (7, 8) of EPH pushbutton (5).For this purpose, the base terminals of changeover switches (11) and(12) are connected to terminal points (7) and (8). The switching polesof changeover switches (11) and (12) are in contact with first resistorR1 in the home position of pushbutton (5) and with second resistor R2 inthe actuated condition of pushbutton (5). Changeover switches (11) and(12) can be actuated together with first key T1.

Moreover, a further resistor R3 in series with a further switch (15) isdisposed in parallel with resistors R1 and R2. Upon actuation of switch(15) by second key T2, further resistor R3 bridges across terminalpoints (7, 8). As a result, the trailer checking position (describedhereinafter) is engaged. Because of the rigid coupling of keys T1 and T2by rocker (25) (see FIG. 1), only changeover switches (11, 12) or onlyfurther switch (15) can be actuated.

The cited resistors typically have values of R1=40 kohm, R2=4 kohm,R3=20 kohm.

As mentioned hereinabove, further switching group 2 of pushbutton (5) isused to increase the reliability by redundancy, and it containscorresponding changeover switches (13, 14) as well as further switch(16). This has terminal points (9, 10) and is connected via connectinglines (3, 4) to ECU (6).

To EPH pushbutton (5) with its switching groups 1 and 2 there isconnected a common multicore cable containing connecting lines (1, 2)and (3, 4), respectively. This leads to evaluating electronic unit (6)(EPH ECU), which can be disposed at any desired location in the vehicle.Within ECU (6), the cited cables (1) and (3) are connected by means of aresistor RH to battery voltage UB. The lower connecting lines (2) and(4) are connected to the frame via a further resistor RL.

By virtue of this circuit, a voltage divider is formed which is composedof resistor RH, the internal resistance of the EPH pushbutton, which isdifferent depending on how the switches are actuated, and resistor RL,and which is energized by battery voltage UB.

By means of voltage subdivision by further resistors RM1 and RM2, outputpotentials UH and UL are formed which correspond to the usual inputvoltage range of microcontrollers. As described in greater detailhereinafter, these voltages are sensed in analog form by evaluatingelectronic unit (6) of the EPH, examined for faults and used for controlof the electropneumatic parking brake or parking brake of the vehicle.

FIG. 3 illustrates, in normalized form from zero to 100 percent, somepossible voltage potentials of UH and UL that may result duringundisturbed or disturbed operation of pushbutton (5). UL is illustratedin the lower half and UH in the upper half of the diagram.

As shown in the diagram, UL is equal to 12.5 percent and UH is equal to87.5 percent when the EPH pushbutton is in home position.

In the switched condition of the EPH pushbutton, or in other words whenkey T1 is activated, UL is equal to 37.5 percent and UH to 62.5 percent.This is the case because the value of second resistor R2 is onlyapproximately one tenth of the value of first resistor R1.

For the trailer checking position, or in other words when key T2 isactivated, UL is equal to 25 percent and UH to 75 percent.

In different fault situations of the pushbutton or of the connectinglines, various potentials occur for UL and UH. These are measured andevaluated in analog form by the ECU. As a result, the respective faultscan be identified and indicated by an appropriately programmed logicunit.

Three specific faults are shown in the diagram of FIG. 3.

In the case of a short circuit in the cable, or in other words of aconnection between connecting lines (1, 2) or (3, 4), a common potentialof 50 percent occurs for UL and UH.

In the case of a cable break in connecting lines (1) or (2) in theillustrated unactuated condition of the EPH pushbutton, UL is equal tozero percent and UH to 100 percent.

In the case of a short circuit of one of the two connecting lines (1) or(2) to the battery, a potential of 100 percent occurs for the faultyline.

In the case of a short circuit of one of the two connecting lines (1) or(2) to the frame, a potential of zero percent occurs for the faultyline.

Other faults of combined nature result in potentials within the rangebetween zero and 100 percent and can therefore be distinguished by ECU(6).

If ECU (6) detects a fault, this is signaled to the operator by aseparate fault indicator (not illustrated), and the functional scope ofthe EPH is restricted appropriately such that a safe condition isreached for the vehicle.

FIG. 4 shows the same circuit as FIG. 2, but with an additional wake-updevice for the ECU. This comprises two operational amplifiers (20, 21),whose control terminals are connected via further resistors RM3 toconnecting lines (2) and (4) respectively.

Upon actuation of one of keys T1 or T2, the respective control terminalof operational amplifiers (20, 21) receives voltage, and, so, a wake-upsignal is generated at the output.

This circuit expansion yields the advantage that the ECU has to be underoperating voltage not constantly but only when the EPH function or thetrailer checking position is engaged.

The trailer checking position permits the operator to experiment withreleasing the trailer brakes when the tractor vehicle is parked togetherwith a trailer on a slope, and both parts of the vehicle train are beingheld by the parking brake. As a result, the operator can determinewhether the brakes of the tractor are sufficient alone in this situationto hold the vehicle train stationary. If this proves not to be the case,the operator can further secure the train by underpinning with a brakewedge.

FIG. 5 illustrates a simplified embodiment of switching group 2 of EPHpushbutton (5), wherein switching group 2 is effective without resistorsR1 and R2. Rather, there are provided two parallel switches (22, 23),which for actuation are closed by key T1 and thereby short circuitconnecting lines (3, 4). Connecting line (4) is shorted to the framewithin the ECU. The connected EPH ECU detects the actuated condition ofswitches (22, 23) by the fact that input voltage UD drops to zero.

This alternative has the advantage that no closed circuit current flows(as would take place through resistor R1 in switching group 1) and thatresistors R1 and R2 can be dispensed with.

Nevertheless, additional complexity is introduced into this alternativeby the fact that a capacitor C1 must be connected in parallel in orderto prevent wear of the contacts of switches (22, 23). A further featureof capacitor C1 is that it discharges through switches (22, 23) whenthey are closed, thus achieving cleaning of the contacts.

Furthermore, because of the absence of closed circuit current inconnecting lines (3, 4), these need to be checked sporadically by meansof a test circuit (26), for which purpose input terminal (27) ofconnecting line (3) is forced to zero potential. In the case of intactlines (3, 4), a characteristic falling voltage curve of input voltage UDis recorded due to the discharge of capacitor C1 via the internalresistances of connecting lines (3, 4) and of test circuit (26), andthis is evaluated by the ECU.

Otherwise the circuit according to FIG. 5 corresponds to the circuitaccording to FIG. 2.

1. A pushbutton, especially for actuating an electropneumatic parkingbrake (EPH) in road vehicles, with an evaluating electronic unit (ECU)(6), which is connected via connecting lines (1, 2) or (3, 4) and whichis used for evaluation of the pushbutton as well as for activation ofthe EPH, characterized in that the potentials of the connecting lines(1, 2) or (3, 4) of the pushbutton (5) are evaluated in order that theECU (6) can detect switch positions and/or faults of the pushbutton (5).2. A pushbutton according to claim 1, characterized in that there areprovided two parallel, identical, mechanically coupled switching groups(switching group 1 and switching group 2), which can be actuatedtogether by means of a first key (T1) in order to apply and release theparking brake (EPH) alternately.
 3. A pushbutton according to claim 1 to2, characterized in that the two switching groups 1 and 2 each containtwo changeover switches (11, 12; 13, 14), which are connected via theirbase to the connecting lines (1, 2; 3, 4) and which, via their switchingpoles, each make contact with a first resistor R1 when the pushbutton(5) is in home condition.
 4. A pushbutton according to claim 3,characterized in that the switching poles of changeover switches (11,12; 13, 14) in the actuated condition make contact with a secondresistor R2 in parallel with resistor R1, the value of the secondresistor R2 being approximately 1/10 of the value of the first resistorR1.
 5. A pushbutton according to one or more of claims 1 to 4,characterized in that the two switching groups 1 and 2 each contain afurther resistor R3, which bridges over the terminal points (7, 8) or(9, 10) of the pushbutton (5) upon actuation of further switches (15,16) disposed in series.
 6. A pushbutton according to claim 5,characterized in that the two further switches (15, 16) are mechanicallycoupled and can be actuated by means of a second key T2, which is usedto engage a trailer checking position.
 7. A pushbutton according to oneor more of claims 1 to 6, characterized in that keys T1 and T2 aremechanically coupled with one another in the form of a rocker (25).
 8. Apushbutton according to one or more of claims 1 to 7, characterized inthat, inside the electronic unit (ECU) (6), the connecting lines (1) to(4) of the pushbutton (5) are each connected via a resistor RH to theon-board voltage UB or via a further resistor RL to the frame.
 9. Apushbutton according to claim 8, characterized in that the potentials(UH, UL) of the connecting lines (1, 2, 3, 4) are measured and evaluatedin analog form by the electronic unit (ECU) (6) after subdivision byfurther resistors RM1, RM2.
 10. A pushbutton according to claim 1 to 9,characterized in that two further lines (17, 18) are routed back fromthe ECU (6) to the pushbutton (5) to provide the operator with a statusindication about the electropneumatic parking brake.
 11. A pushbuttonaccording to claim 10, characterized in that the status indication isachieved by a signal light (24) built into the pushbutton (5).
 12. Apushbutton according to one or more of claims 1 to 11, characterized inthat there is provided, for the electronic unit (ECU) (6), a wake-updevice (19), which generates a wake-up signal upon actuation of thepushbutton (5).
 13. A pushbutton according to claim 12, characterized inthat the wake-up device (19) comprises two operational amplifiers (20,21), whose signal inputs are each connected via a further resistor RM3to the connecting lines (2, 4).
 14. A pushbutton according to one ormore of claims 1 to 13, characterized in that a simplified switchinggroup without the resistors R1, R2 is provided instead of one or bothswitching groups 1, 2, wherein, upon actuation of the key T1, theconnecting lines 3, 4 of the simplified switching group can be connectedby means of two switches (22, 23) disposed in parallel.
 15. A pushbuttonaccording to claim 14, characterized in that a capacitor C1 is connectedin parallel with the switches (22, 23).
 16. A pushbutton according toclaim 14 to 15, characterized in that the input terminal (27) of theconnecting line (3) can be forced to zero potential by means of a testcircuit (26).